Method of molding products from moist materials and apparatus realizing same

ABSTRACT

Products are molded in a mold assembled prior to molding from a lower punch and a mold case arranged in coaxial relationship, the mold being subjected, in the course of charging it with the material, to harmonic vibrations whereby the material undergoes precompaction, and the subsequent compaction of the material by the combined effect of a vertical vibratory shock load and a compressive load is aided by vibrating the mold case, the vertical vibratory shock load being applied to the material via the lower punch. The apparatus for molding products according to the method of the invention incorporates power cylinders mounted on a base, with an additional crosshead being suspended by elastic members on the rods of said power cylinders, said additional crosshead being adapted to reciprocate along the columns of the apparatus, and the additional crosshead mounts vibration exciters and a mold case, whereas the vibrating frame carries the lower punch mounted in coaxial relationship with the mold case.

This is a divisional of application Ser. No. 760,436, filed Jan. 13,1977, now U.S. Pat. No. 4,140,744, which in turn is a continuation ofapplication Ser. No. 529,531 filed Dec. 4, 1974 now abandoned.

FIELD OF THE INVENTION

The present invention relates to a method of molding moist materials aswell as to an apparatus for producing the method.

BACKGROUND OF THE INVENTION

The instant invention can be used in metallurgy, in the manufacture ofrefractories, ceramics and in other industries for molding products frommetallic and cermet powders, molding and core sands, refractory andceramic mixtures, etc.

The moist mixtures employed in molding are known to comprise aparticulate component with binders, wetting agents and other additives,for which reason such mixtures are known as moist or bulk mixtures.

It is known in the art to mold products, e.g. slabs and items ofpredominantly simple shape and small height, from moist bulk mixtures byvibratory compaction thereof in a mold. The known method comprisescharging a mold, made up of a case rigidly secured to a bottom and anupper punch, with a moist mixture and exerting a downward compressivelead on the mixture via the upper punch. After the mold is charged withthe mixture it is subjected to an upwardly-directed vibratory shockload, while the downward compression pressure is simultaneously raisedto a maximum (cf. USSR Inventor's Certificate No. 264,956, Cl. 80a, 49).

In order to raise the product density, the process of vibratorycompaction is effected at a compressive load-to vertical vibratory shockload ratio of 0.4 to 0.7.

In the prior art technique, the mold is filled with the moist mixturenon-uniformly due to the low mobility of the mixture as well as the lackof any means for uniformly distributing the mixture about the mold. Thisdisadvantage is particularly significant if the products to be moldedhave a large height, small cross-section and an intricate configuration.

With the mold non-uniformly filled with the mixture, the molded productnaturally exhibits a non-uniform pattern of density distribution with aresultant deterioration of quality. In order that the mold may be moreeffectively filled with the mixture during charging, the mixture israked and levelled in the course of charging, which increases aboutconsumption and reduces the efficiency of the molding process.

The products molded according to the known method with the mold case andbottom being rigidly interconnected and subjected to vibratory shockloading show a considerable degree of non-uniformity of densitydistribution. Hence, if their density is to be more uniformlydistributed, it is necessary to increase the force of vibrations and thecompression pressure as well as to prolong the time during which thematerial being compacted is exposed thereto. These factors increase insignificance with the height of the product. As a result, the quality ofthe products deteriorates and the efficiency of the process drops.Additionally, the power consumption rises, entailing higher costs.

It is likewise known in the art to employ a vibratory-shock device formolding products from moist bulk materials, e.g. casting, molds, whichcomprises a vibrating frame with a vibration exciter, said framemounting power cylinders which drive a mobile crosshead carrying anupper punch. The power cylinders simultaneously serve as guide columnsfor the mobile crosshead with the upper punch. The mold with the lowerpunch is secured directly on the vibrating frame. As the mold and thelower punch are rigidly anchored to the vibrating frame, thisinstallation cannot be employed for molding products over 150 mm inheight, because density non-uniformity in such items will exceed theallowable limit. Additionally operation of this known installationunavoidably involves hard manual labor in assembling and disassemblingthe mold and removing the molded products, which adds to the labor costsand detracts from the efficiency of molding.

SUMMARY OF THE INVENTION

It is an object of the present invention to eliminate the foregoingdisadvantages.

The invention provides a method of molding products from moist materialsthat ensures high quality of the molded products, and an apparatus formolding products from moist materials that is conducive to a higheroperating efficiency, lower power consumption and lower production costfor the products.

Accordingly, a method of molding products from moist materials,primarily refractory and and ceramic material is provided by chargingthe mold with the material and compacting simultaneously exposing thematerial to a vertical vibratory shock load applied from below and acompressive load applied to the material from above via the upper punch,whereby, in accordance with the invention, a mold assembled prior tomolding from a lower punch and a case is used, the two elements beingcoaxially arranged, and the mold is subjected, in the course ofcharging, to harmonic vibrations which precompact the material. Thesubsequent compaction of the material by the combined effect of theupward vertical vibratory shock load and the downward compressive loadis effected by additionally vibrating the mold case, the vertical shockvibrations being transmitted to the material via the lower punch.

The molding operation should preferably be carried out at a ratio of thedownward compressive load to the upward vibratory shock load of 0.1 to0.35, and at a difference of vibration amplitude between the mold caseand the lower punch of 0.2 to 0.5 mm.

In an apparatus according to the invention, a vibrating frame isinstalled through an elastic padding on a base and carries columns whichare connected in the upper portion thereof by a stationary crossheadwith a power cylinder, whereof the rod carries a mobile crosshead withan upper punch, mounted on the base are power cylinders, with anadditional crosshead suspended by means of elastic members on the rodsof said power cylinders, said additional crosshead which is adapted toreciprocate along the columns carries a vibration exciter and a moldcase, while a lower punch is secured on the vibrating frame coaxiallywith the mold case.

The inventive idea of the present invention resides in the following:

While molding moist materials in a mold comprising a case, a lower punchand an upper punch disconnected one from another, it is possible toexpose the material being compacted to a variety of different loadsvarying in magnitude depending on the particular step of the process,with the result that high-quality products are manufactured at highoperating efficiency with a minimum of power input and at a minimum ofcost.

The mold is charged with the material and the latter in precompacted byimparting to the mold harmonic vibrations in the course of charging.Under the effect of these mold vibrations, the moist material acquiresmobility, thereby permitting the charging process to be accelerated andthe mold to be filled uniformly, even in case of very high andintricately shaped products, dispensing with manual labour; such anapproach likewise enables the material in the mold to be precompacted.Additionally, the precompaction leads to a considerable reduction inheight of the material with which the mold is charged, which permitscutting down the molding time, thereby adding to the operatingefficiency of the entire procedure.

The subsequent compaction of the material in the mold is effected bymeans of shock vibrations applied to the material being molded frombelow and creating a pressure P₁ thereon, as well as by means of acompression pressure P₂ applied from above, and finally with the aid ofvibrations applied through the lateral sides of the mold. The vibratoryshock load is transmitted to the material by the lower punch; thecompressive load by the upper punch; and the lateral load by the moldcase. The mold case vibrations sharply reduce the effective coefficientof friction of the material against the case walls, so that the materialis compacted by the combined effect of vibratory shock loading andcompressive loading at a considerably reduced friction of the materialagainst the lateral surfaces of the mold. Owing to this feature, it ispossible to provide for a high and uniform density of the products atlow values of compressive and vibratory shock loads and within aminimized process time.

The combined effort exerted on the material being compacted, made up ofthe lateral vibrations, the vibratory shock load from below and thecompressive load from above, not only raises the intensity of the forceexerted on the material but also reduces the effective coefficient offriction inside the material and raises its mobility. Owing to thisfeature, it is possible to uniformly compact the material even whenmolding products of intricate shape, large height and smallcross-section, requiring minimal compressive and vibratory loading and aminimum of time.

The above features are particularly pronounced in cases where the ratioof the compressive load P₂ exerted on the material from above to thevertical vibratory shock load P₁ applied to the material from below (P₂/P₁) lies within the range from 0.1 to 0.35. At P₂ /P₁ ratios smallerthan 0.1, the upper punch vibrations will be unstable and theirfrequency will be less than that of the vibrations applied from below,so that the intensity of the vibratory lead on the material and, hence,the efficiency of the process will be reduced. At P₂ /P₁ ratios inexcess of 0.35, the upper punch will stay in permanent contact with thematerial so that the material will be exposed to vibratory shock loadingonly from below, causing a one-sided pattern of compaction, with theresult that density differential will increase with the height of theproduct.

Lateral vibrations are most effective in minimizing the coefficient offriction between the material and the mold case where the amplitude A₁of mold vibrations exceeds the amplitude A₂ of lower punch vibrations bya value in the range from 0.2 to 0.5 mm. At a vibration amplitudedifference (A₁ -A₂) less than 0.2 mm., the coefficient of friction willbe reduced negligibly and the effect of the lateral vibrations on thematerial will be increased by a very small margin, resulting in reducedequidensity, heightwise, and overall density of the molded product; thisalso prolongs the compaction time which, in turn, detracts from theefficiency of the molding process. At an amplitude difference (A₁ -A₂)more than 0.5, the interplay of the upward shock vibrations and thelateral vibrations will upset the stability of vibrations of the moldcase and the lower punch, drastically minimizing their effect on thematerial being molded, with the result that the density of the productdiminishes and the compaction process time increases.

The invention will be further understood from the following specificexample illustrative of the proposed method.

EXAMPLE 1

It is required to manufacture saggers for recovering iron powder fromcasting skin, which are formed as pipes of external diameter 510 mm,internal diameter 450 mm and height 310 mm. The starting material is amoist silicon-carbide mixture comprising loan and sulphite-alcoholstillage as a binder taken in respective amounts of 3 and 7 percent byweight of the silicon carbide base. The mold comprises disconnectedpunches, an upper and a lower one, and a mold case made up of an innerand outer portions interconnected in four places by means of blocksspaced 90° about the circumference of the case. The lower punch providedwith blind longitudinal slots is so fitted in the clearance between theinner and outer portions of the case that the blocks are received in theslots thereof.

The mold is charged with the moist material and is simultaneouslysubjected to harmonic vibrations generated by electromechanicalexciters, the frequency of case vibrations being 50 Hz and the vibrationamplitude difference between the case and the lower punch being 0.4 mm.In the course of charging, the material is thus precompacted by 15percent. The material is further compacted by the combined effects ofmold vibrations, a pressure P₂ equal to 1.8 kg/sq.cm. exertedcompressively from above, and a pressure of 15 kg/sq.cm. exerted on thematerial from below, the P₂ /P₁ ratio being 0.12. The compaction processlasts 25 seconds.

The products thus manufactured have a mean apparent density of 2.60g/cu.cm. and a density differential through the product volume within0.06 to 0.08 g/cu.cm.

EXAMPLE 2

It is required to manufacture guides for cementation furnaces, eachguide formed as a parallelpiped measuring 575 by 180 mm in plan view and90 mm in height having two bevelled edges measuring 80 by 30 mm alongthe long side on one lateral surface thereof. The starting material is amoist silicon-carbide mixture of the following composition, wt.%:

silicon carbide, 80;

crystalline silicon, 20; and

alcohol solution of bakelite of density 1.16 g/cu.cm. (binder), 7.5.

The binder is an extra component not included in the dry power weight.The mold comprises three independent elements: a lower punch, an upperpunch and a case. The operations of charging and precompaction areperformed along the lines set down in the previous example.

The step of final compaction is effected by the combined effect of moldvibrations, a compressive load P₂ equal to 2.5 kg/sq.cm. exerted fromabove and a vibratory pressure P₁ equal to 7.8 kg/sq.cm. exerted on thematerial from below, the P₂ /P₁ ratio being 0.32. The compaction time is10 to 15 seconds. The products have a mean apparent density of 2.70g/cu.cm. and a density differential through the product volume of notgreater than 0.05 g/cu.cm.

EXAMPLE 3

It is required to manufacture supports for the roasting of ceramics,formed as I-beams 200 mm in length and 200 mm in height, having a flangewidth of 100 mm and a web thickness of 25 mm. The starting material is amoist silicon carbide mixture of a composition identical with that givenin Example 1. Just as in the previous two examples, the mold comprises alower punch, an upper punch and a case disconnected one from another. Incross-section, the punches and the mold case are formed as I-beams.

The charging and precompaction steps are carried out as in Example 1.The final compaction step is likewise effected as in Examples 1 and 2except that the compression pressure P₂ is equal to 2.1 kg/sq.cm. andthe pressure P₁ exerted from below is equal to 8.4 kg/sq.cm., i.e. theP₂ /P₁ ratio is equal to 0.25. The compaction time is 20 seconds. Theproducts have a mean apparent density of 2.62 to 2.64 g/cu.cm. and adensity differential through the product volume of not greater than 0.06g/cu.cm.

The invention will be better understood from the accompanying drawingsillustrating a preferred embodiment thereof, wherein:

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a front elevation of an apparatus for molding saggers forrecovering iron powder from casting skin, saggers partially in section;and:

FIG. 2 is a side of the apparatus of FIG. 1

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawings, the apparatus comprises a base 1 (FIGS. 1and 2) mounting a rubber padding 2. Mounted on the padding 2 is avibrating frame 3 with columns 4 secured therein. A stationary crosshead5 is fitted in the upper portion of the columns 4, the crosshead 5carrying a power cylinder 6 secured therein, the rod 7 of the powercylinder 6 carrying a mobile crosshead 8 with an upper punch 9. On thebase 1 there are mounted power cylinders 10, rods of which 11 mount,through springs 12, an additional crosshead 13 on which securedelectromechanical vibration exciters 14 and a mold case 15. Thevibrating frame 3 is pressed against the rubber padding 2 by clamp means16. The vibrating frame mounts two electromechanical unbalance vibrationexciters 17 with unbalancing members 18. A lower punch 19 is secured inthe vibrating frame 3. The mold case 15 comprises two coaxially arrangedcylindrical members 20 and 21 interconnected in the bottom portionthereof by blocks 22 at four points uniformly spaced about thecircumference of the mold case 15. The mold case is so disposed that thelower punch 19 is received in the clearance between the cylindricalmembers 20 and 21, thereby defining a bind-bottom cavity to receive themolding mixture on charging. The vibrating frame 3, the columns 4 andthe stationary crosshead 5 are interconnected one with another to form arigid structure which provides for the precision of displacement of themobile crosshead 8 with the upper punch 9 as well as of the additionalcrosshead 13 with the mold case 15 as they reciprocate relative to thelower punch 19. In the initial position, the mobile crosshead 8 (FIGS. 1and 2) with the upper punch 9 as well as the additional crosshead 13with the mold case 15 are found in their extreme upper positions, themembers 20 and 21 of the mold case together with the upper cavity of thelower punch 19 defining a cavity for receiving mixture 23 upon charging.

Operation of the above-described, apparatus illustrates the proposedmethod of molding products, e.g. saggers as follows:

The mold is charged, mechanically or manually, with a required amount ofmoist silicon-carbide mixture. The vibration exciters 14 (FIG. 1) areactuated; the unbalance shafts thereof rotate in opposite directions,imparting vertically-directed vibrations to the additional crosshead 13suspended by the springs 12 and carrying the mold case 15. Acted upon bythese vibrations, the moist material uniforms fills the cavity of themold and simultaneously undergoes preliminary compaction.

The hydraulic cylinder 6 is actuated to lower the mobile crosshead 8with the upper punch 9. While moving downward, the upper punch 9compacts the material 23 in the mold; simultaneously, the mold case 15with the additional crosshead 13 moves downward, fitting over the lowerpunch 19. As the additional crosshead 13 moves downwards, the rods 11force the working fluid from the hydraulic cylinders 10. Electric motors24 (FIG. 2), which drive the vibration exciter 17, are switched on, saidmotors 24 transmitting rotation via clutches 25 to a synchronizer 26which retates, through cardan shafts 27, the unbalance shafts 18 of thevibration exciter 17 in opposite directions, said synchronizer 26 alsosynchronizing the rotations of said shafts in terms of speed and phase.Thereby the vibrating frame 3 together with the lower punch 19 securedthereon is driven into directional vertical vibration. Acted upon by theexciter 17, the vibrating frame 3 is detached from the elastic padding 2and then is forced downward by the weight of the vibrating parts of theapparatus (the vibrating frame 3, the lower punch 19, the columns 4, theupper crosshead 5, the power cylinder 6 and the vibration exciter 17) aswell as by the action of springs 28 of the clamp means 16 to strikeagainst the elastic padding 2 which adds to the amplitude andacceleration of vibrations. Time is provided a vibratory shock mode, farmore effective than harmonic vibrations as far as compaction efficiencyis concerned. So, the material in the mold experiences the shockvibrations applied from below by the punch 19, the downward compressiveload created by the upper punch 9, as well as the lateral vibrationsgenerated at the inner and outer side surfaces and applied to thematerial through the mold case members 20 and 21. Under the effect ofall these vibrations, the material in the mold is rapidly and uniformlycompacted to a desired density.

20 to 25 seconds later (the time is set depending on the product sizeand the composition of the mixture) the electric motors are switchedoff, and the unbalance shafts of the vibration exciters 14 and 17 ceaserotating, signifying the end of the compaction process.

The hydraulic cylinder 6 raises the mobile crosshead 8 with the upperpunch 9 to its extreme upper position, while the hydraulic cylinders 10lower the additional crosshead 13 with the mold case 15 downward,releasing the molded product from the mold. At the instant the hydrauliccylinders 10 are actuated, the electric motors driving the vibrationexciters 14 are also switched on. With the mold case 15 vibrating whilethe molded product is being released from the mold, the required effortis considerably reduced and the operation is speeded up, therebyreducing the wear of the mold members 20 and 21. As soon as the upperedge of the product emerges from the mold case, the vibration exciters14 are deenergized.

The product (sagger) left on the lower punch 19 is removed from theapparatus and delivered to the next step of the process (drying),whereupon the additional crosshead 13 with the mold case 15 is raised toits extreme upper position.

The cycle of sagger molding is over, and the apparatus is ready for thenext cycle.

The capacity of the apparatus amounts to 40 to 45 products per hour. Asis evident from the description, the proposed method for moldingproducts from moist materials and the apparatus realizing same providefor the manufacture of quality products at a high operating efficiency.

What is claimed is:
 1. An apparatus for molding products from moist bulkmaterials comprising:a base; an elastic padding mounted on said base; avibrating frame resting on said elastic padding; a fastening means forfastening said vibrating frame to said base; columns secured on saidvibrating frame; a stationary crosshead interconnecting said columns inthe upper portion thereof; a power cylinder comprising a rod and apiston mounted on said stationary crosshead, said rod extending beyondsaid stationary crosshead in a downwardly direction; a mobile crossheadattached to said rod of said power cylinder guided by said columns; anupper punch secured to said mobile crosshead; a lower punch secured onsaid vibrating frame; further power cylinders comprising further rodsand further pistons being mounted on said base; an additional crossheadmounted on said further rods and adapted to reciprocate and be guidedalong said columns; vibrations exciters mounted on said vibrating frameand said additional crosshead; a power means for powering said vibrationexciters; and a mold case mounted on said additional crosshead, saidmold case, said upper punch, and said lower punch being arrangedcollinearly.